The present invention relates to a brushless fan motor and a counter-rotating axial flow fan comprising two brushless fan motors.
A brushless fan motor disclosed in Japanese Patent Publication No. 2003-230246 (Patent Document 1) includes a rotor, a stator arranged inside the rotor, and an impeller arranged outside the rotor. The rotor includes a rotor cover and a plurality of permanent magnet magnetic pole portions. The rotor cover includes a cylindrical portion and an end plate portion integrally formed at one end of the cylindrical portion and fixed to a rotary shaft. The permanent magnet magnetic pole portions are disposed on an inner circumferential surface of the cylindrical portion. The impeller includes a plurality of blades and a cap member having the blades mounted thereon. The cap member includes a cylindrical peripheral wall portion having the blades which are mounted on an outer peripheral portion of the peripheral all portion, and a bottom wall portion that is disposed at an end of the peripheral wall portion and faces the end plate portion of the rotor cover. The cap member is fit with the rotor cover. In the brushless motor of such a type, dissipation of heat generated in the stator to the outside is a problem to be solved especially when the number of rotation of the rotor is increased.
To solve this problem as described above, Japanese Patent Publication No. 10-210727 (Patent Document 2) has disclosed a motor. In the disclosed motor, an end plate portion of a rotor cover made of a metal is partially cut and raised, thereby forming a plurality of vanes. In this motor, when a rotor is rotated, ambient air is introduced inside the rotor cover by means of the vanes. The introduced ambient air is heated by heat generated in a stator and dissipated to the outside. As a result, the temperature inside the motor will decrease.
However, in the brushless fan motor of a dual structure where the cap member is fit with the rotor cover, it is difficult to reduce the temperature of the rotor cover itself. Further, in the structure where the vanes are formed on the rotor cover, the vanes may come into contact with winding portions of a stator unless assembly accuracy between the rotor cover and the stator and forming accuracy of winding portions of the stator are enhanced. For this reason, it is necessary to ensure sufficient spacing between the end plate portion of the rotor cover and the stator. This hinders reduction in dimension of the brushless fan motor in an axial direction.
An object of the present invention is to provide a brushless fan motor and a counter-rotating axial flow fan, in which cooling effect on a stator may be enhanced and of which the dimension in an axial direction may also be reduced, without requiring high assembly accuracy.